Chemical and electrochemical studies of borane anions and metallaboranes
Several new monosubstituted anionic derivatives of [B₃H₈]⁻ of the type [B₃H₇(X)]⁻(X = NCSe, NCBPh₃, NCBH₂NCBH₃, NCB₃H₇,NCBH₂CN and NCBH₂CNB₃H₇) have been prepared. The disubstituted anions [B₃H₆(Cl)(X)]⁻(X = NCBH₂NCBH₃, NCBH₂CN and NCB₃H₇) and [B₃H₆(Br) NCB₃H₆(Br)]/⁻ have also been prepared and studied by various spectroscopic techniques. Two-dimensional n. m. r. spectroscopy was shown to be useful in the qualitative determination of the bonding employed in these anions. The electrochemical properties of these anions have been investigated by various techniques. It was found that when the substituent was varied the oxidative stability of the anions varied. Metallaboranes of some of these anions have been prepared by anodic dissolution of a suitable metal in a solution of the anion. The structures and dynamics of substituted derivatives of the [B₉H₁₄]⁻ ion have been studied. The anions [B₉H₁₃(X)⁻(X = CINCSe, NCBPh₃, NCBH₂NCBH₃, NCBH₂CN, NCBH₂CNB₉H₁₃, CN, and NCAgCNB₉H₁₃) and [B₉H₁₂(CN₂]⁻ have been prepared. ¹¹B and ¹H n. m. r. spectroscopy indicated that when the substituent contained electron withdrawing groups (e. g. the hydrogen atoms on NCBH₂NCBH₃) the anion was static at room temperature on the n. m. r. time scale. If no electron withdrawing groups were present on the substituent then the molecule was fluxional at room temperature on the n. m. r. time scale. The electrochemistry of these anions was also studied and it was found that, in some cases, oxidation resulted in cage closure to give substituted nido-derivatives. Anodic dissolution of Cu or Ag in solutions of some of the anions produced metallaboranes. The chemistry and electrochemistry of [B₉H₁₂]⁻ was also studied and the crystal structure of the (N(PPh₃)₂]⁺ salt was obtained. Several new substituted metallaboranes have been prepared by reaction of the substituted octahydrotriborate (1-) or substituted tetradecahydrononaborate (1-) anions with Cu(PPh₃)₂(BH₄). The reactions of Mn(CO)₅ Br with [B₉H₁₃(X)]⁻(X = NCSe, NCBH₂NCBH₃ and NCBPh₃) have also been investigated.